Review of the micro and Macro mechanisms of gel-based plugging agents for enhancing oil recovery of unconventional water flooding oil reservoirs

In recent years, gel plugging agents had made significant contributions to addressing water channeling and water flooding issues in water-flooded oil reservoirs. To meet the demands of unconventional and complex oil reservoirs for profile control and water blocking processes, the performance and adaptability requirements of gel-based profile control agents were increasingly stringent. This paper summarized the macroscopic effects and microscopic mechanisms of different types of gel plugging agents in the processes of "injection, migration, plugging, and stabilization", explored the shortcomings of existing research, and innovatively proposes directions for future research. Firstly, existing gel plugging agents faced challenges in achieving deep plugging in oil reservoirs with large well-spacing. In response, we proposed an innovative approach using high phase-change stable oil-in-water emulsions as carriers, along with in-situ generated dispersed gel particles under reservoir conditions, to achieve "long-distance and long-lasting" profile control in oil reservoirs with large well-spacing. Secondly, current research mainly focused on enhancing the temperature and salinity resistance of gel plugging agents through the addition of nanomaterials, temperature and salinity-resistant functional monomers or groups, with limited exploration of the microscopic mechanisms. There was a lack of research focusing on the specific locations, patterns, and mechanisms of polymer chain breakage, hindering the targeted resolution of the challenge of polymer gel molecules' long-term profile control difficulty under high-temperature and high-salinity conditions. Lastly, future researches should consider the adsorption losses of gel systems in complex reservoirs, design their composition and dosage, establish adsorption prediction models, simulate the loss mechanisms and quantities in reservoirs, and determine the minimum concentration required for effective plugging. These research outcomes were expected to significantly optimize the performance of profile control agents and drive innovation in the application of gel plugging agents in high-temperature and high-salinity oil reservoirs with large well spacing, providing robust theoretical and practical support for the development of future profile control and water blocking technologies.